Tuning oxygen vacancies in two-dimensional iron-cobalt oxide nanosheets through hydrogenation for enhanced oxygen evolution activity

The oxygen evolution reaction (OER) represents the rate-determining step of electrocatalytic water splitting into hydrogen and oxygen. Creating oxygen vacancies and adjusting their density has proven to be an effective strategy to design high-performance OER catalysts. Herein, a hydrogenation method is applied to treat a two-dimensional (2D) iron-cobalt oxide (Fe₁Co₁O_x-origin), with the purpose of tuning its oxygen vacancy density. Notably, compared with Fe₁Co₁O_x-origin, the iron-cobalt oxide hydrogenated at 200 °C and 2.0 MPa optimized conditions exhibits a markedly improved OER activity in 1.0 M KOH (with an overpotential η of 225 mV at a current density of 10 mA·cm^–2) and a rapid reaction kinetics (with a Tafel slope of 36.0 mV·dec^–1). Moreover, the OER mass activity of the hydrogenated oxide is 1.9 times that of Fe₁Co₁O_x-origin at an overpotential of 350 mV. The experimental results, combined with density functional theory (DFT) calculations, reveal that the optimal control of oxygen vacancies in 2D Fe₁Co₁O_x via hydrogenation can improve the electronic conductivity and promote OH^– adsorption onto nearby low-coordinated Co³⁺ sites, resulting in a significantly enhanced OER activity. [Figure not available: see fulltext.].